Question

我有一张名为＆＃39; ward_councillors＆＃39;和两列＆＃39; ward＆＃39;和＆＃39;议员＆＃39;。该表包含所有议员及其负责的病房的清单。每个病房有三名议员，我需要做的就是分组，这样我每个病房都有一个不同的记录和三个新的栏目，三个议员分别负责该病房。

例如目前有：

WARD   | COUNCILLOR
ward a | cllr 1
ward a | cllr 2
ward a | cllr 23
ward b | cllr 4
ward b | cllr 5
ward b | cllr 8

试图实现：

WARD    | COUNCILLOR 1| COUNCILLOR 2| COUNCILLOR 3
ward a  | cllr 1      | cllr 2      | cllr 23
ward b  | cllr 4      | cllr 5      | cllr 8

提前致谢，克里斯

Answer 1

我倾向于使用条件聚合来处理这种类型的查询：

select ward,
       max(case when seqnum = 1 then councillor end) as councillor1,
       max(case when seqnum = 2 then councillor end) as councillor2,
       max(case when seqnum = 3 then councillor end) as councillor3
from (select wc.*,
             row_number() over (partition by ward order by councillor) as seqnum
      from ward_councillors wc
     ) wc
group by ward;

Answer 2

我的sqlFiddle存在问题，但是我在本地postgres上写了这个：

CREATE TABLE ward_councillors (
  ward VARCHAR
  , councillor VARCHAR
);

INSERT INTO ward_councillors
VALUES 
('ward a', 'cllr 1')
, ('ward a', 'cllr 2')
, ('ward a', 'cllr 23')
, ('ward b', 'cllr 4')
, ('ward b', 'cllr 5')
, ('ward b', 'cllr 8')
;


SELECT * 
FROM crosstab('SELECT ward, null /*doesnt really matter*/, councillor  FROM  ward_councillors') 
    AS (ward VARCHAR, councillor_1 VARCHAR, councillor_2 VARCHAR, councillor_3 VARCHAR, councillor_4 VARCHAR)
;

似乎输出你想要的东西：

  ward  | councillor_1 | councillor_2 | councillor_3 | councillor_4
--------+--------------+--------------+--------------+--------------
 ward a | cllr 1       | cllr 2       | cllr 23      |
 ward b | cllr 4       | cllr 5       | cllr 8       |
(2 rows)

这里全部描述：http://www.postgresql.org/docs/9.1/static/tablefunc.html#AEN142967

分组依据并添加列

2 个答案: